The present disclosure relates generally to intrusion detection systems, and particularly to radio detection and ranging (RADAR) intrusion detection systems.
There is a need for security devices to monitor areas subject to penetration by trespassers and also to alert authorities when personnel have entered a hazardous zone. One commonly employed technique is that of electromagnetic RADAR. It is well known in the art that a RADAR system may be used to monitor an area even though there is no direct visible line of sight from the RADAR unit to the area under surveillance, as a RADAR signal may often successfully penetrate and return through common building materials, thereby allowing the RADAR unit to be hidden or inconspicuous.
For an electromagnetic emitter such as a RADAR unit, it is important to select an appropriate frequency band for operation. There are many bands that may be used but most of them require a license for operation. Bands that do not require a license, providing that radiation limits comport to regulations, are known as the Industrial, Scientific, and Medical, or ISM bands. These bands allow unlicensed electromagnetic radiation across a number of relatively wide spectrum bands. In the United States three of these bands are from 902-928 MHz, 2400-2483.5 MHz (also herein referred to as the 2.4 GHz band), and 5725-5850 MHz (also herein referred to the 5.8 GHz band).
One complication in using the ISM bands is that the user may interfere with other users, or be interfered with by other users. It is common that some of the ISM spectrum that may be used to support surveillance RADAR may also be used for an office local area network (LAN), for example. The use of RADAR may interfere with the LAN and severely impair the LAN's ability to transport data without error. Alternatively, the LAN may interfere with the surveillance RADAR's ability to detect intruders at the desired false alarm/missed detection receiver operating characteristic curve.
Building materials and the nature of the building construction may also pose serious operational problems so far as attenuation is concerned. Radiation in the ISM band from 2400-2438.5 MHz exhibits approximately the same amount of loss on propagation as radiation in the ISM band from 5727-5850 MHz through drywall but exhibits four to five decibels (dBs) less attenuation through cinder blocks.
There is therefore a need to devise surveillance RADAR systems that can more effectively function in light of these problems and shortcomings of the present systems in the art.